This invention relates to an optical communication apparatus connected between an optical communication medium, and an information processor, and to an optical communication method using this apparatus. More particularly, the invention relates to an optical communication apparatus useful in transmitting optical signals between electronic devices such as a computer and a terminal unit or within these electronic devices
Conventional electrical communication systems which rely primarily upon metallic conductor cables are being replaced in greater number by optical communication systems in which devices are interconnected by optical fiber cables or the like so that information may be transmitted between these devices in the form of optical signals. The reason for this is that optical communication systems possess such important advantages as the ability to transmit information in large volume and little susceptibility to the adverse effects of electromagnetic noise and the like. These systems are being employed widely especially in the field of communication by specific transmission circuit networks and pay station circuit network.
Optical communication systems are now finding use especially in the field of information transmission between individual information processors that deal with a comparatively small amount of information. For example, these systems are being utilized for communication between electronic devices such as a computer and an automatic controller, a LAN node and a terminal unit or a host computer and a terminal computer These systems also find use as means for transmitting signals within these devices.
However, when an optical communication is employed for signal transmission between or within such devices, an optical communication apparatus required for special-purpose optical transmission must be separately provided as a substitute for the interface of the conventional electrical communications system.
In order to construct this optical communication apparatus, it is necessary to provide an electro-optical converter circuit drive unit for driving an electro-optical converter circuit adapted to convert electrical signals from a processor, the electro-optical converter circuit (a light-emitting element or the like), an opto-electrical converter circuit (a light-receiving element or the like), and an amplifier circuit for amplifying the signal from this circuit Also required is a driving power supply for operating each of these components.
Owing to the need for these special-purpose components, the already existing electrical communication apparatus cannot be used as is for optical communication. In other words, optical communication using this apparatus is impossible without adding on special components and power supply equipment This is a disadvantageous requirement in terms of space and cost in comparison with the electrical communication systems used so far.
When it is attempted to achieve optical communication with the existing apparatus, an optical transmission adapter having power supply equipment for obtaining the necessary power from a special-purpose commercial power source must be separately connected to the apparatus, after which the apparatus is connected to an optical fiber cable or the like.
The construction of this conventional adapter for optical transmission is illustrated in FIG. 9. Shown in FIG. 9 are an optical communication apparatus 1, optical communication connectors 8, 9, fiber cables 10a, 10b for optical communication, a power supply section 14, an AC adapter 15, a plug 16 and an information processor 20. For optical communication in two directions, an electric signal S1 for information transmission from the information processor 20 is sent to a light-emitting element drive circuit 4 through an electrical connector 2 and a receiver circuit 3a in an interface circuit 3. The signal S1 is converted into a corresponding optical signal by a light-emitting element 5, and the optical signal is delivered to the optical fiber cable 10a via the optical communication connector 8 to be transmitted to a light-receiving element in an electronic device at the destination
An optical signal sent via the optical fiber cable 10b from a light-emitting element in the electronic device of another party is received by a light-receiving element 7 via the optical communication connector 9 to be converted into an electric signal Following amplification by an amplifier circuit 6, the signal is transmitted as a received signal to a signal line S2 of the information processor 20 via a driver circuit 3b of the interface 3 and the electrical connector 2.
In such signal transmission and reception, the power supply unit 14 supplies all of the power needed to drive the electro-optical converter section which includes the light-emitting element drive circuit 4 and the light-emitting element 5, the opto-electrical converter section which includes the amplifier circuit 6 and the light-receiving element 7, and the receiver circuit 3a and driver circuit 3b of the interface circuit 3.
The supply of power to the power supply unit 14 is achieved by connecting driving DC power, obtained by converting commercial AC power into DC power via the AC adapter (AC-DC converter) 15, to a power supply receptor 17 of the optical communications apparatus power supply unit 14 via a plug 16. Alternatively, the necessary power can be received from the information processor 20 via a special-purpose power supply line P without the plug 16 from the AC adapter 15 being inserted into the power supply unit 14.
The power supplied to the power supply unit 14 is subjected to a voltage conversion to output power of +V1 at a first terminal thereof. Also, power .+-.V2 is produced as an output via an internal filter circuit, which comprises an inductor L and capacitors C4, C5, and an internal DC-DC converter 18.
The +V1 power is supplied to the light-emitting element 5, the light-receiving element 7, the drive circuit 4 that drives the light-emitting element 5, and the amplifier circuit 6 that amplifies the electric signal from the light-receiving element 7. The .+-.V2 power is supplied to the receiver circuit 3a and driver circuit 3b of the interface circuit 3.
A direct brightness modulation/demodulation system having a comparatively simple circuit construction is employed as the signal modulation/demodulation system at the time of the electro-optical conversion and opto-electrical conversion.
An example of this direct brightness modulation/demodulation is as shown in FIG. 10(A) and 10(B). At the time of transmission, as illustrated in FIG. 10(A), an electric signal sent by the information processor 20 and received by the receiver circuit 3a is transmitted from the latter to the drive circuit 4, which causes the light-emitting element 5 to emit light in such a manner that the pulse duty time of the electric signal inputted to the driver circuit 4 is made to correspond to the light emission time of the element 5. At the time of reception, as shown in FIG. 10(B), the optical signal received by the light-receiving element 7 is converted (demodulated) into an electric signal the pulse duty time whereof corresponds to the light reception duty time. After amplification in the amplifier circuit 6, the electric signal is sent to the information processor 20 via the driver circuit 3b.
Thus, in the conventional optical communications apparatus, all of the power necessary for driving the interface circuit 3, the electro-optical converter circuit comprising the drive circuit 4 and light-emitting element 5 and the opto-electrical converter circuit comprising the amplifier circuit 6 and the light-receiving element 7 must be separately furnished externally via a specially provided power supply unit.
In other words, it is necessary to specially provide an output of power from within the information processor 20 or to furnish an arrangement for obtaining DC power from a specially provided commercial AC power supply to drive the apparatus.
As a result, it is necessary to adopt a configuration in which the information processor 20 is equipped with a special optical transmission arrangement or a configuration in which an AC power supply terminal is separately provided and a special-purpose AC-DC converter. Either alternative is disadvantageous in that the overall cost and size of the optical communication apparatus are increased.
Furthermore, since the signal modulation/demodulation system employs direct brightness modulation/demodulation in the conventional optical communication apparatus, the light-emitting element, which consumes the most power within the apparatus, is required to emit light continuously during the high or low pulse duty time of the inputted electric signal for transmission. Consequently, the power consumed ranges from several hundred milliwatts to several watts. Reducing this power consumption constitutes a problem in the prior art.
As disclosed in U.S. Pat. No. 4,534,039 and U.S. Pat. No. 4,677,646, inventions have been proposed in which the required power is formed from an input control signal line and a received signal is converted into a corresponding output signal, whose specifications are those of a desired interface, by the power acquired from the control signal line However, this art is used in converting one electric signal into another, which ordinarily requires little consumption of power, and cannot be employed in an apparatus that performs an electro-optical conversion consuming a large amount of power at the time of light emission.